The present invention relates generally to an apparatus for testing the balance of wheels for automobiles and small trucks, and it relates more particularly to new and improved means for mounting wheels on such apparatus.
The accuracy of a balancer is limited by the degree to which the apparatus used to mount the wheel on the spindle of the balancer prevents deviation between the axis of rotation of the wheel and the longitudinal axis of the spindle of the balancer. For example, if a wheel of the type utilized on a typical passenger automobile is tilted as little as 0.005 inches (0.13 mm) at the mounting holes of the wheel from a plane perpendicular to the longitudinal axis of the spindle the balance results may be off one ounce (0.03 kg) on each side of the wheel. Displacement of the wheel in a direction perpendicular to the axes of the wheel and spindle of the wheel by 0.010 inches (0.26 mm) will cause the balance results to be off one ounce (0.03 kg). Even this small of an imbalance condition will cause a ride vibration problem on some vehicles.
It is now a common practice in the wheel balancing art to align a wheel relative to the longitudinal axis of the spindle of the balancer by using a centering member having a frustoconical outer surface provided with a central bore which fits closely over the spindle to permit the centering member to slide on the spindle without tilting. The diameter of the centering member at the end closest to the fixed end of the spindle is greater than the diameter of the center hole of a wheel that is to be balanced. and the diameter at the other end is less than the diameter of the center hole of the wheel to be balanced. The wheel is slipped over the free end of the spindle to the point where it has an interference fit on the centering member, and is then secured in place by a collar that is threadably attached to the spindle. This type of mounting system works very well with central hole centered type wheels because the vehicle designers use the central holes of central hole centered type wheels to center, or pilot, the wheels on the axle hubs of a vehicle. Mounting bolts are then used to secure the wheel in position on the vehicle. Since the bolt holes in these wheels are not used for centering the wheel on the axle, they should not be used for centering the wheel on a balancer.
However, the use of mounting hole centered type wheels has presented a problem with respect to wheel balancing because in such wheels the central hole is not used to center, or pilot, the wheels on the axle hubs of a vehicle. Mounting hole centered type wheels may have mounting holes in a pattern that will fit several brands of automobiles having different sizes of axle hubs, so the central holes of these wheels are purposely made to have a diameter larger than the axle hubs of at least some of the vehicles that these wheels may be mounted upon. Such wheels therefor are aligned with the axle hub by accurately located mounting holes. One problem with this mounting system is that the mounting holes in the wheel may wear in an eccentric manner during the use of the wheel on a vehicle, and merely relying on the precision of the mounting holes when mounting the wheel on a balancer may yield inaccurate results. These mounting hole centered type wheels also rely upon the perpendicularity of the surface of the wheel containing the mounting holes on the side of the wheel intended to engage the axle hub to the longitudinal axis of the axle as a means for indexing the alignment of the wheel on the axle.
The present invention provides an apparatus for mounting a wheel on a balancer that takes advantage of both the accuracy of the location of the mounting holes of the wheel and the precision of the surface of the wheel containing the mounting holes to give the smallest possible deviation between the axis of rotation of the wheel and the longitudinal axis of the spindle of the balancer.